Thermoregulation

The infant is especially vulnerable to hypothermia (see also Chapter 40 ) because of both the large ratio of body surface area to weight and a limited ability to cope with cold stress. Cold stress will result in increased oxygen consumption and can cause metabolic acidosis. A premature infant is even more susceptible because of very thin skin and limited fat stores. The infant may compensate by means of shivering and nonshivering (cellular) thermogenesis. The minimal ability to shiver during the first 3 months of life makes cellular thermogenesis (metabolism of brown fat) the principal method of heat production.^[40] It is very important to address all aspects of possible heat loss during anesthesia, as well as during transport to and from the operating room. Heat lost by conduction is reduced by placing the baby on a warming mattress and warming the operating room. Heat lost through convection is minimized by keeping the infant in an incubator, covered with blankets. The head should also be covered. Heat lost from radiation is decreased by the use of a double-shelled isolette during transport. Heat lost through evaporation is lessened by humidification of inspired gases, the use of plastic wrap to decrease water loss through the skin, and warming of skin disinfectant solutions. Hot air blankets are particularly useful.^[41] Anesthetic agents can alter many thermoregulatory mechanisms, particularly nonshivering thermogenesis in neonates.^{[42] [43]} Infants may have an increased metabolic rate (without protein catabolism) for up to 12 hours postoperatively.^[44]